U.S. patent number 4,257,795 [Application Number 05/893,863] was granted by the patent office on 1981-03-24 for compressor heat pump system with maximum and minimum evaporator .delta.t control.
This patent grant is currently assigned to Dunham-Bush, Inc.. Invention is credited to David N. Shaw.
United States Patent |
4,257,795 |
Shaw |
March 24, 1981 |
Compressor heat pump system with maximum and minimum evaporator
.DELTA.T control
Abstract
An air source heat pump system incorporating a refrigerant
charged bulb within the air flow passing over the outdoor coil of
the heat pump system to sense outside ambient air temperature. The
refrigerant charged bulb supplies a variable saturated pressure
which acts upon a bellows of a control unit whose opposite side is
subjected via a second bellows to saturated suction pressure
(corresponding to refrigerant evaporating temperature) of the
refrigerant returning from the outdoor coil to the inlet of the
compressor. The bellows provides a spring load. An electrical
switching device responsive to this pressure differential acts to
first block unnecessary loading of the compressor and secondly to
initiate unloading of the compressor. Additional switching means
prevents excessive unloading of the compressor and insures
subsequent initiation of loading to prevent liquid logging of the
evaporator coil.
Inventors: |
Shaw; David N. (Unionville,
CT) |
Assignee: |
Dunham-Bush, Inc. (West
Hartford, CT)
|
Family
ID: |
26275984 |
Appl.
No.: |
05/893,863 |
Filed: |
April 6, 1978 |
Current U.S.
Class: |
62/150; 62/209;
62/228.1 |
Current CPC
Class: |
F25B
1/047 (20130101); F25B 30/02 (20130101); F25B
49/022 (20130101); F25B 47/006 (20130101); F25B
2600/026 (20130101); F25B 2500/07 (20130101) |
Current International
Class: |
F25B
1/04 (20060101); F25B 49/02 (20060101); F25B
30/00 (20060101); F25B 47/00 (20060101); F25B
1/047 (20060101); F25B 30/02 (20060101); F25D
021/00 (); F25B 041/00 (); F25B 001/00 () |
Field of
Search: |
;62/150,156,228C,209,227,151,160,159 ;165/29 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Wayner; William E.
Assistant Examiner: Tanner; Harry
Attorney, Agent or Firm: Sughrue, Rothwell, Mion, Zinn and
Macpeak
Claims
What is claimed is:
1. In an air source heat pump system of the type including a first
heat exchanger forming an indoor coil, a second heat exchanger
forming an outdoor coil and positioned in an ambient air flow, a
compressor, and conduit means carrying a refrigerant and connecting
said compressor between said coils and in a closed series loop, an
expansion means provided within the conduit means adjacent to the
inlet end of the outdoor coil to permit the outdoor coil to act as
an evaporator when the system is in the heating mode, and wherein
means are provided for loading and unloading the compressor to vary
the capacity of the compressor and the system compression ratio,
the improvement comprising:
(a) temperature sensing means positioned adjacent the outdoor coil
and within the ambient air flow passing over the outdoor coil;
(b) means for sensing the evaporating temperature of the
refrigerant available to the compressor from the outdoor coil;
and
(c) control means operatively connected to said sensing means and
responsive to a predetermined temperature decrease of evaporating
temperature below ambient temperature for at least preventing
further loading of the compressor, thereby tending to prevent the
outdoor coil surface temperature from dropping below the dew point
and virtually eliminating frosting of said outdoor coil.
2. The air source heat pump system as claimed in claim 1 wherein
said control means comprises means for controlling the loading and
unloading means of the compressor and responsive to a predetermined
rise in temperature of the evaporating refrigerant available to the
compressor toward ambient to block said means for unloading the
compressor to prevent further unloading of the compressor, and
responsive to a slightly higher temperature rise of suction
refrigerant toward ambient to cause operation of said means for
loading the compressor to initiate compressor loading.
3. The air source heat pump system as claimed in claim 1, wherein
said control means constitute first means in response to a
predetermined temperature drop of the evaporating temperature of
the refrigerant available to the compressor toward ambient
temperature to a predetermined degree for controlling said means
for loading the compressor to initially block further loading of
the compressor, second means to initiate unloading of the
compressor at a slightly further decrease in the evaporating
temperature of the refrigerant toward that of ambient, third means
responsive to initial rise of evaporating temperture towards
ambient to a predetermined degree for initially controlling said
unloading means for blocking unloading of said compressor, and
fourth means for controlling said compressor loading means to
initiate loading of the compressor when the evaporating temperature
rises further with respect to the ambient temperature above that
which initiates operation of said unload blocking means, and to
thereby prevent logging of the outdoor coil.
4. The air source heat pump system as claimed in claim 2 wherein
said control means comprises means for comparing the ambient
temperature to the evaporating temperature of the refrigerant
available to the compressor from the outdoor coil, said comprising
means comprises spring-biased bellows means, and said control means
further comprises switch means responsive to bellows means movement
for controlling the loading and unloading means of said
compressor.
5. The air source heat pump system as claimed in claim 3 wherein
said control means comprises means for comparing the ambient
temperature to the saturated suction temperature of the refrigerant
available to the compressor from the outdoor coil, said comparing
means comprises spring-biased bellows means, and said control means
further comprises switch means responsive to bellows means movement
for controlling the loading and unloading means of said
compressor.
6. The air source heat pump system as claimed in claim 4 wherein
said compressor comprises a helical screw rotary compressor, said
capacity control means comprises a capacity control slide valve for
said compressor, a hydraulic cylinder and piston assembly is
operatively coupled to said slide valve for shifting the slide
valve between extreme positions corresponding to full compressor
loading and unloading, said system comprises a source of hydraulic
pressure fluid, load and unload solenoid valves for selectively
supplying and relieving said fluid pressure to chambers to
respective sides of a power piston within the cylinder to shift
said slide valve towards and away from said extreme positions, an
electrical voltage source, and said switch means comprises a first
switch operatively mounted adjacent said bellows means and being
responsive to an initial bellows means movement to disconnect the
load solenoid valve from said electrical voltage source, and a
second switch operatively positioned with respect to said bellows
means and responsive to further movement of said bellows means from
its initial movement position in the same direction for connecting
said unload solenoid valve to said electrical voltage source,
whereby, operation of said first switch prevents energization of
the load solenoid valve and loading of the compressor, while
subsequent operation of said second switch effects energization of
the unload solenoid valve to direct hydraulic pressure fluid
through said unload solenoid valve to said cylinder and piston
assembly to inititate unloading of the compressor.
7. The air source heat pump system as claimed in claim 5 wherein
said compressor comprises a helical screw rotary compressor, said
capacity control means comprises a capacity control slide valve for
said compressor, a hydraulic cylinder and piston assembly is
operatively coupled to said slide valve for shifting the slide
valve between extreme positions corresponding to full compressor
loading and unloading, said system comprises a source of hydraulic
pressure fluid, load and unload solenoid valves for selectively
supplying and relieving said fluid pressure to chambers to
respective sides of a power piston within the cylinder to shift
said slide valve towards and away from said extreme positions, an
electrical voltage source, and said switch means comprises a first
switch operatively mounted adjacent said bellows means and being
responsive to an initial bellows means movement and responsive to
initial movement of said bellows means to disconnect the load
solenoid valve from said electrical voltage source, and a second
switch operatively positioned with respect to said bellows means
and responsive to further movement of said bellows means from its
initial movement position in the same direction for connecting said
unload solenoid valve to said electrical voltage source, whereby
operation of said first switch prevents energization of the load
solenoid valve and loading of the compressor while subsequent
operation of said second switch effects energization of the unload
solenoid valve to direct hydraulic pressure fluid through said
unload solenoid valve to said cylinder and piston assembly to
initiate unloading of the compressor.
8. The air source heat pump system as claimed in claim 7 wherein
said control means further comprises a third switch operatively
positioned with respect to said bellows means and responsive to an
initial movement of said bellows means to a predetermined degree in
opposition to the direction of movement causing operation of said
first switch, for disconnecting the unload solenoid valve from said
electrical voltage source, and a fourth switch operatively
positioned with respect to said bellows means and responsive to
further movement of said bellows means from the position causing
actuation of said third switch and in the same direction, for
connecting said load solenoid valve to said electrical voltage
source and for initiating compressor loading to thereby prevent
logging of the outdoor coil when the evaporating temperature
closely approaches ambient temperature.
9. The air source hat pump system as claimed in claim 8 wherein
said indoor coil is mounted within an enclosure for conditioning
the enclosure space, and said system further comprises a two-step
thermostat having a below set point normally open switch and an
above set point normally open switch with said below set point and
above set point switches closing in sequence as the temperature
within the space to be conditioned rises and defining an enclosure
temperature differential therebetween, and means for connecting
said below set point switch in series with said second switch means
and said load solenoid valve and across said voltage source and
said above set point switch being connected in series with said
third switch and said unload solenoid valve and across said voltage
source, such that the temperature of said space is modulated
between said set point conditions by energizing said load solenoid
valve when the space temperature decreases below the set point
condition of said first set point valve and said above set point
switch effects operation of said unload solenoid valve and unloads
the compressor when the temperature within the enclosure reaches a
predetermined temperature above the below set point condition, and
wherein said first, second, third and fourth switches constitute
overrides for the two-step thermostat.
10. The air source heat pump system as claimed in claim 9 further
comprising an override switch for selectively connecting said load
solenoid valve across said voltage source to permit quick pull-up
space temperature by operating the compressor under full load and
energization of the load solenoid valve in deference to said
control operation provided by said first, second, third and fourth
switches and said above and below set point switches.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to heat pumps, and more particularly, to a
heat pump system involving simplified controls for maximizing
system coefficient of performance, while insuring that safe
operating limits are not exceeded.
2. Description Of The Prior Art
Heat pump systems comprise indoor and outdoor coils within a
refrigeration loop including a compressor, with the coils trading
functions as condensor and evaporator depending upon requirements
for heating or cooling of the enclosure housing the indoor coil.
Thus, during heating mode, the outdoor coil constitutes an air
source evaporator, and the indoor coil acts as a condensor to heat
the enclosure, while during the cooling mode, the indoor coil
becomes a system evaporator and the outdoor coil becomes the air
source condensor. The present invention is concerned with achieving
a high coefficient of performance for a heat pump system when the
system is operating under heating mode, and the outdoor coil acts
as the system evaporator and the indoor coil as the system
condensor.
Sometimes there occurs a situation where the heat pump systme
operates over extended periods with great differences between the
coil surface temperature and with the ambient temperature above
that which is necessary for effective heating of the building when
the system is under heating mode. This is also important in terms
of the number of defrost cycles required to defrost the outdoor
coil which functions as the evaporator for the system.
It is therefore an object of the present invention to provide a
heat pump control system wherein the saturated suction pressure to
the compressor is never allowed to fall further than that which is
necessary to adequately heat the building in question and which
prevents the saturated condensing pressure from exceeding that
which is necessary to adequately heat the building under
steadystate conditions.
It is a further objection of this invention to provide an improved
air source heat pump system in which the coefficient of performance
of the heat pump system is maximized at operating conditions.
It is a further object of the present invention to provide an
improved air source heat pump system in which the coil surface
temperature is prevented from dropping below the dew point or wet
bulb temperature so that, under most conditions, no frosting occurs
on the outdoor coil acting as the evaporator for the system, and to
virtually eliminate the necessity for defrosting.
SUMMARY OF THE INVENTION
The present invention is directed to an air source heat pump system
of the type including a first heat exchanger forming an indoor
coil, a second heat exchanger forming an outdoor coil, and
preferably positioned in heat exchange relation to the ambient air,
a compressor, and conduit means carrying a refrigerant and
connecting said compressor between said coils and in a closed
series loop. An expansion valve or capillary tube is provided
within the conduit means adjacent to the inlet end of the outdoor
coil to permit the outdoor coil to act as an evaporator when the
system is in a heating mode. Means are provided for loading and
unloading the compressor to effect capacity control of the
compressor. The improvement comprises a bulb positioned adjacent
the outdoor coil and within the ambient air flow passing over the
outdoor coil, with the bulb carrying a mass of refrigerant
corresponding to that within said conduit means. The bulb and said
conduit means, at a point intermediate the outside coil and the
inlet to the compressor, are connected to a sensor for comparing
the ambient temperature at the outside coil to the saturated
suction or evaporating temperature of the refrigerant at the
outdoor coil, available to the compressor. Control means responsive
to the comparing means acts to at least prevent further loading of
the compressor in response to a temperature differential of
predetermined magnitude. Preferably, the control means constitutes
a two-step control, which first blocks further loading of the
compressor and which secondly initiates unloading of the compressor
at a slightly higher temperature differential than that required to
block further loading.
The means for comparing the ambient temperature to the saturated
suction temperature of the refrigerant at the outlet of the outdoor
coil and available to the compressor comprises a bellows means, and
the control means comprises switch means responsive to bellows
means movement for controlling the loading and unloading means of
the compressor. The compressor may comprise a helical screw rotary
compressor, and the capacity control means may constitute a slide
valve. A hydraulic cylinder and piston assembly may be fixed to the
slide valve for shifting the slide valve between extreme positions
corresponding to full compressor loading and unloading,
respectively. The system may comprise a source of hydraulic
pressure fluid and load and unload solenoids for selectively
supplying pressure fluid to and relieving such pressure fluid from
chambers to the sides of the power piston within the cylinder to
shift the slide valve to effect compressor loading and unloading.
Said switch means may comprise a first, normally closed microswitch
adjacent the bellows means and responsive to initial bellows means
movement to disconnect a load solenoid connected thereto from its
electrical source, and a second, normally opened microswitch within
a circuit including an unload solenoid and said electrical source,
such that upon displacement of the bellows means to a further
degree, and the normally open microswitch closes to energize the
unload solenoid and cause the hydraulic pressure fluid from the
source to be directed to the power piston to shift the slide valve
towards unload position under the second step of a two-step
control.
The control device may incorporate third and fourth microswitches
for initially preventing further unloading of the compressor by
opening, in a first step, the circuit to the unload solenoid and
subsequently, in a second step of the control operation, cause
change of state closing of the fourth microswitch to close the
electrical circuit between the source and the load solenoid valve,
such that hydraulic pressure fluid directed to the power piston
shifts the slide valve towards load position to effect some loading
of the compressor to prevent liquid refrigerant logging of the
evaporator coil.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a hydraulic schematic circuit diagram of an air source,
helical screw compressor, heat pump system incorporating the
maximum and minimum evaporator .DELTA.T control as one embodiment
of the present invention.
FIG. 2 is an electrical schematic diagram of the electrical control
circuit employed in the illustrated embodiment of the invention of
FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention is illustrated in conjunction with a heat
pump system which incorporates a helical screw rotary compressor as
an element thereof. However, the invention has equal application to
air source heat pump systems involving other forms of compressors,
such as reciprocating compressors and the like. The control scheme
provided to the heat pump system, which is of typical construction,
prevents extended operation of the heat pump system at differences
between coil surface temperatures and ambient temperatures greater
than that which is necessary for effective heating of the building
or interior within which the indoor coil is positioned. In that
respect, the principal components of the air source heat pump
system of the present invention comprises an outdoor coil indicated
generally at 10, a helical screw rotary compressor indicated
generally at 12, which may be of the hermetic type and which may
include within the hermetic casing an electric motor for driving
the helical screw rotors, an indoor coil 14 which is provided
within an enclosure or building 16 being conditioned; the
compressor 12 being located intermediate of the outdoor coil 10 and
the indoor coil 14. Conduit means indicated generally at 18 connect
the outdoor coil 10, the compressor 12 and the indoor coil 16 in a
closed series refrigeration loop in that order. For the purposes of
illustration, the heat pump system is shown under conditions where
it operates solely in a heating mode --that is, the outdoor coil 10
acts as the evaporator for the system and the indoor coil 14 acts
as the condensor. A four-way valve or similar means is simply
eliminated in this illustrated embodiment. As such, there is a
requirement for a restriction within the conduit means 18 at the
inlet to the outdoor coil 10 acting as the evaporator and the
system incorporates a thermal expansion valve 20 for this purpose,
although, obviously, a capillary tube or similar means could be
provided. The conduit 18 carries a suitable refrigerant, such as
R22, R500 or the like, with the refrigerant in vapor form being
compressed by compressor 12 and discharged under high pressure
where it condenses within the indoor coil 14, giving up heat to the
interior or space within the enclosure 16 being conditioned. The
condensed liquid refrigerant passes through conduit means 18 to the
thermal expansion valve 20 where the refrigerant expands and
absorbs heat which is removed from the air passing over the
surfaces of the outdoor coil 10 as shown by arrows 22, this air
flow being induced by means of a plurality of motor-driven fans
indicated generally at 24. The compressor 12 is provided with
capacity control means taking the form of a slide valve 26 which
covers a portion of the compressor casing 28 and which controls the
extent compression of the suction gas which enters the compressor
at inlet 30 and which discharges at outlet 32, the slide valve
being shiftable longitudinally, as indicated by the double-headed
arrow 34. A shift to the right acts to unload the compressor while
a shift to the left acts to load the compressor. This is achieved
by a hydraulic piston and cylinder assembly indicated generally at
36, including a cylinder 38 within which piston 40 reciprocates,
the piston defining a chamber 42 to the left and a chamber 44 to
the right, the piston being connected mechanically to the slide
valve by a mechanical connection such as shaft 46. Schematically,
in order to effect loading and unloading of the compressor
therefor, it is necessary to supply a pressurized fluid to one of
the chambers 42 or 44 of the piston and cylinder assembly 36 and
remove fluid from the opposite chamber, such as 44, and vice versa.
For instance, to achieve unloading of the compressor, the
pressurized fluid, such as hydraulic liquid, is fed to chamber 44,
causing the piston to shift from right to left, with the slide
valve moving towards the full load position, reached by slide valve
26 shifting to its leftmost position. Appropriate stops are
provided for limiting the movement of the slide valve. Such
apparatus is conventional, and also conventionally, solenoid
operated valves are employed for controlling the connection between
chambers 42 and 44 and a source of pressurized fluid, such as a
hydraulic oil or the like, the source being indicated schematically
at 48. In this respect, and for illustrative purpose only, there is
shown an unload solenoid valve 50 and a load solenoid valve 52, the
unload solenoid 50 being connecting by way of conduit means 54 to a
fluid pressure source 48, which opens to chamber 42 of the piston
and cylinder assembly 36. Similarly, the load solenoid 52 acts to
connect the right-hand chamber 44 of the piston and cylinder
assembly 36 to the source of fluid pressure 48 by way of conduit
56, carrying valve 52.
While the load and unload solenoid valves may be appropriately
otherwise controlled by suitable means (not shown) to insure
operation of the heat pump system in response to certain load
conditions, such as by way of the temperature, for instance, within
the enclosure 16 being conditioned and being controlled through a
suitable thermostat (not shown) within that enclosure, the present
invention is directed, in part, to a particular control scheme for
insuring that the heat pump system will operate to prevent the
saturated condensing temperature within the indoor coil 14, acting
as a condensor for the system, from exceeding that which is
necessary to adequately heat the enclosure 16 under steady-state
conditions. In that regard, the system incorporates a special
control device as at 58 which constitutes a closed casing or
housing 60 carrying a first bellows 62 which spans across a portion
60a the housing and forms with housing portion 60a, a first chamber
63. A second chamber 65 is formed onto opposite side of the control
device by housing portion 60b and a second bellows 64. The inner
ends 62a and 64a of bellows 62 and 64, respectively, are
interconnected by rod 66, which constitutes a means for comparing
the pressures within the chambers 63 and 65. In that regard, the
chamber 63 is connected by way of a capillary tube 68 to a bulb 70
which is mounted adjacent to the outdoor coil 10, within the air
flow path of the ambient air 22 and preferably on the inlet side of
that unit. Also, preferably, the bulb 70 is shielded from the
sunlight so that it may truly sense the temperature of the ambient
air available to the outdoor coil 10 for supplying heat to that
coil under heat pump system heating mode. The bulb 70 is preferably
charged with a refrigerant identical to that within the closed
series refrigeration loop provided by conduit 18, such as R- 500.
Thus, the refrigerant charged bulb 70 will supply a variable
saturated pressure (correlated to ambient temperature) which acts
through the capillary tube 68 and by way of the upper chamber 63 on
the bellows 62 to vary the set point of end 62a of that bellows as
a function of the outdoor ambient air temperature feeding the
system evaporator as provided by outdoor coil 10. The bellows 62
and 64 each have a spring constant. Alternatively, if the bellows
are not of a spring material, they may house compression springs.
Preferably, the spring constant is fixed, but set point may be
adjustable to provide an adjustable spring load to an actuator bar
or blade 72 fixed to rod 66 and extending at right angles thereto,
intermediate of the ends of the rod. A conduit 77 connects chamber
65 of bellows 64 to conduit means 18 at point 78 intermediate of
the outdoor coil 10 and inlet 30 to the compressor 12. Thus,
chamber 65 is always subject to saturated suction pressure
available to the compressor corresponding to the evaporating
temperature of the refrigerant within the outdoor coil 10. A
microswitch 74 is firstly mounted within casing 60 such that its
actuator button 80 underlying an adjustment screw on blade 72 is
somewhat more remote from that screw than an actuator button 82
carried by a second microswitch 76 from a second adjustment screw
71 carried by blade 72. Preferably, the actuator blade 72 extends
beyond the microswitches 74 and 76, and the control system
advantageously includes additional microswitches, as at 84 and 86
and the blade 72 carrying adjustment screws 85 and 87 which overly,
respectively, actuator buttons 89 and 91 for microswitches 84 and
86. The adjustment screws 69, 71, 85 and 87 may be suitably,
axially screwed to adjust their lower ends relative to the actuator
buttons 80, 82, 89 and 91, respectively, for microswitches 74, 76,
84 amd 86. The rod 66 which extends axially between the bellows 62
and 64 constitutes the pressure comparing means for the control
device 58. Therefore, depending upon the saturated vapor pressure
of the refrigerant within bulb 70 and responsive to ambient
temperature, and the saturated vapor pressure of the refrigerant at
the suction side of the compressor, the blade 72 will shift towards
or away from the fixed microswitches to effect depression or
projection of the actuator buttons of the microswitches and a
change of state of the microswitches.
Referring to FIG. 2, microswitch 74 is connected in series
electrically to coil 51 of the unload solenoid valve 50 by way of
leads 90 and across an electrical source defined by lines 92. In
turn, the microswitch 76 is connected by way of leads 88, in series
with coil 53 of load solenoid valve 52 and across the voltage
source. Microswitch 74 constitutes a normally open switch, while
microswitch 76 constitutes a normally closed switch. In a typical
system operation involving microswitches 74 and 76 alone, the
control device 58 functions to prevent a maximum difference between
the outside ambient air temperature and saturated suction
temperature from being exceeded. As an example, if the air 22
flowing over the outdoor coil 10 is at 0.degree. F., the saturated
suction temperature of the refrigerant within line 18 available
from the outdoor coil 10 for compression by compressor 12 should
not be allowed to drop below -20.degree. F. Under the same control
at 20.degree. ambient, the saturated suction should not be allowed
to drop below 6.degree. F., and at 40.degree. ambient, the control
device 58 should operate to prevent the saturated suction from
dropping below 30.degree. F. In contrast, with no controls, at a
40.degree. ambient and a compressor operating under full load
conditions, the saturated suction temperature may drop as low as
-20.degree. F., with 40.degree. ambient air blowing over the
outdoor coil 10. It is obvious that the efficiency of the system is
destroyed under such conditions.
For instance, as the evaporating saturated suction pressure as seen
within chamber 65 of bellows 64 falls 10 psi below the saturated
pressure of the refrigerant provided by bulb 70 and sensed within
chamber 63 at the opposite bellows 62, the rod will be shifted
vertically downwards depressing adjustment screw 70 carried by
blade 72 and actuator button 82 of the microswitch 76, causing that
switch to shift from its normally closed contact condition to open
contact condition and opening the circuit between the electrical
source and coil 53 the load solenoid 52, thus preventing further
loading of the compressor by preventing the pressure fluid from
passing from source 48 to chamber 44 and shifting the slide valve
further, from right to left.
As the system continues to operate and the evaporating pressure
tends to fall even further within the outdoor coil 10, a further
pressure drop will be experienced within chamber 65 and the bellows
65 will contract even further, causing blade 72 to be depressed
further, to the extent that adjustment screw 68 depresses button 80
to change the state of microswitch 74 from normally open contact
condition to closed contact condition, thus closing the circuit
from the power source via lines 98 to coil 51 of the unload
solenoid valve 50. This permits pressure fluid to be directed to
chamber 42 through line 56 and causing the piston 40 to shift
towards the right to unload the compressor by shifting the slide
valve 26 to the right.
From the above, it is evident that the control device 58 will
function such that the differential sensing element --that is, the
rod 66 and blade 72-- will always actuate the microswitches
dependent upon the temperature differential. However, in a very
cold ambient, it will allow a significant temperature differential
to exist, while in a mild ambient, there will only be allowed a
very mild temperature differential prior to effecting a control
action. This is completely opposite of normal compressor system
characteristics. For instance, if the compressor, absent the
control device, were to run fully loaded in a very cold ambient,
there would be a high differential. If the compressor were to run
fully loaded in a mild ambient, the differential increases
massively, leading to high system inefficiency. Thus, the control
device totally elimintes the normal characteristics of the
compressor under given ambient conditions, and the device may
function as a basic control element for application to helical
screw compressor to heat pump systems incorporating helical screw
rotary compressors, other types of rotary compressors, or
reciprocating compressors and may be readily applied to force
unloading of the compressor or to limit further loading and
blocking other controls which might be compelling the machine to
load.
Turning again to FIG. 1, microswitches 84 and 86, which underly
blade 72 within the control device 58 are likewise sensitive to
movement of blade 72. As may be seen in FIG. 2, in this respect,
the microswitch 84 is a normally open contact switch and
microswitch 86 is a normally closed contact switch. However,
adjustment screws 85 and 87 are screwed downwardly with respect to
the blade or bar 72 to which they are threaded to the extent that
the adjustment screw 85 maintains the actuator button 89 of
microswitch 84 in its depressed state, while adjustment screw 87
maintains the actuator button 91 of the microswitch 86 in its
depressed state. With microswitch 84 being a normally open switch,
its switch contacts, under normal circumstances, with the control
system between the set points of a two-step thermostat IT within
the space or room being conditioned, as at 16 in FIG. 1, are held
closed and a circuit is completed to the unload solenoid valve coil
51, while the depression of the actuator button 91 of microswitch
86, which is a normally closed switch, maintains the switch
contacts open and an open circuit exists, including microswitch 86
and coil 53 of the load solenoid valve 52. Microswitches 84 and 86,
therefore, have their states changed in response to an increase in
the evaporator pressure as sensed by bellows 64 through line 77
leading to the suction side of the compressor relative to the
reference pressure of bellows 62 as defined by the refrigerant
filled bulb 70. As the evaporator pressure rises within chamber 65
of bellows 64 relative to chamber 63 of bellows 62, the rod 66
moves vertically upward, causing the bar or blade 72 to move away
from the multiple microswitches. This movement reaches the extent
where the adjustment screws 85 and 87 rise to cause the microswitch
actuator buttons 89 and 91, respectively, to project to the extent
of changing the state of the switch contacts of switches 84 and 86.
The microswitch 84 is connected by way of leads 51 to coil 51 of
the unload solenoid valve 50 and across the control voltage source
via lines 86, such that projection of the actuator button 89 causes
the contacts of microswitch 84 which previously have been
maintained closed to open, thus opening the circuit from the
voltage source to the unload solenoid valve coil 51 and thereby
preventing furthe unloading of the compressor. Upon continued
movement of the rod 66 and blade 72 upwardly, due to a further
increase in pressure within chamber 65 relative to that within
chamber 63 because the saturated vapor pressure of the refrigerant
within conduit 77 and line 18 extending from the outdoor coil to
the suction or inlet side of compressor 12 increases above the
saturated vapor pressure of the refrigerant within bulb 70 and
available to chamber 62, the plunger or actuator button 91 of the
microswitch 86 projects to the point where the switch contacts of
microswitch 86 change state. The normally closed contact which have
been maintained open by the adjustment screw 87 pressing on the
microswitch actuator button 91 now close, and a circuit is
completed through leads 100 to the coil 53 of the load solenoid
valve 52, causing the compressor to load even though the other
parameters of the system are calling for compressor unloading.
Thus, the function of the control device 58 in this instance is to
prevent liquid logging of the evaporator outdoor coil 10 by way of
accumulation of a large quantity of liquid refrigerant within the
outdoor coil 10 and leading to the inlet or suction port 30 of
compressor 12. As may be appreciated, therefore, the single
refrigerant bearing bulb 70 supplied along with line 77 control
input signals to the control device 58 for actuation selectively of
four different microswitches to insure high system efficiency under
heating mode conditions, both low ambient temperature conditions
and high ambient temperature conditions. Obviously, microswitches
84 and 86 could be placed on the opposite side of the blade or bar
72, with the adjustment screws 85 and 87 being threaded from the
bottom towards the top of device 58, whereby the change of state
for microswitches 84 and 86 would be accomplished by depression of
microswitch actuator buttons 89 and 91 rather than a relaxation or
projection of those buttons by movement of the adjustment screws
away from the microswitches under the illustrated embodiment of the
invention.
As mentioned previously, the control device 58 incorporates
additional switches within lines 88 and 98 to effect normal load
and unload operation of the compressor in response to temperature
change with the enclosure 16 being conditioned. This causes the
sets of dual microswitches 74-76 and 84-86 to operate under a
two-step control scheme. In this respect, a mechanical switch
actuator rod, as at 102, is mechanically coupled to a first movable
switch contact 104 which opens and closes with respect to a fixed
contact 106 for a first switch 105 within line 88 and between the
microswitch 76 and one of the control voltage lines 92. A movable
switch contact 108 is fixed to the opposite end of the rod 102
which contact 108 opens and closes with respect to fixed contact
110 of a second switch 109. The contacts 104 and 106, therefore,
define a first thermostat operated switch 105 and switch contacts
108 and 110 define a second thermostat operated 109. Switch 109 is
located within line 98 and between the microswitch 84 and one line
92 of the control voltage source. Schematically, the thermostat
constitutes a pressure responsive diaphragm forming a part of a
chamber 13 carrying an expandible fluid. Rod 102 is fixed to the
center of diaphragm 112 and moves vertically therewith. Chamber 113
is connected to a thermo bulb 115 forming a part of indoor
thermostat 17 within enclosure 16 by a capillary tube 114 with
chamber 113, tube 114 and bulb filled with a heat expansible fluid.
As the temperature in the enclosure 16 increase, the rod 102 of
control device 58 moves vertically upwardly; as the temperature
decreases, rod 102 moves downwardly. Obviously, other types of
thermostats may be employed in lieu thereof.
Thus, switch 105 functions in a normal sense to control the heating
of the space within enclosure 16 being conditioned by causing
opening of the load solenoid valve 52 by energization of the load
solenoid valve coil 53 with absence of override provision of blade
72 and the pressure differential existing between chambers 63 and
65 of bellows 62 and 64. If the temperature within the room or
space 16 being conditioned drops below a predetermined value, the
switch contact 104 closes on fixed switch contact 106, and the
compressor loads to cause an increase in refrigerant flow through
the system and to the indoor coil. Likewise, switch 109 functions
in response to a temperature increase above a predetermined set
point within the enclosure 16 as sensed by the indoor thermostat
IT. However, obviously, the thermostat operated rod 102 will have
caused contacts 104 and 106 of switch 105 to open prior to closure
of movable contact 108 onto the fixed contact 110 of switch 109 and
energization of the unload solenoid valve coil 51 for unloading of
the compressor. The microswitches 74, 76, 84 and 86, therefore, act
as an override to the normal control via the load and unload
solenoid valves 52 and 50, respectively. In that regard, the
minimum .DELTA.T block comes into play when the compressor
unloading is dictated. If the evaporator pressure rises too high
relative to the reference ambient pressure, unloading is blocked;
and if further rise occurs, loading is initiated. At this point,
the pressure is again in check, loading terminates and the
compressor is then banded in a guaranteed flow condition responsive
to further operating parameters depending upon change in load
conditions. Conversely, if excessive loading occurs, the loading
block comes into play when the evaporator pressure drops too far
relative to the reference ambient pressure (temperature). In this
case, microswitch 76 changes state to open contact condition,
preventing energization of the load solenoid valve. Subsequently,
if a further drop occurs, in the evaporator pressure or if the rise
in the referenced pressure (temperature) occurs, microswitch 74 has
its normally open contacts closed, resulting in energization of the
coil 51 of the unload solenoid valve 50 to unload the compressor
until the preset parameters are again in balance.
A typical setting for the microswitches as determined by the spring
constants of the bellows and the position of adjustment screws 68,
70, 85 and 87 and responsive to given system parameters are
provided by the table below.
______________________________________ VARIABLE .DELTA.P
BLOCK-BELOW SET POINT Assume 20.degree. F. Ambient 21.0 psig R-12
STEP FUNCTION .DELTA.P COIL PSIG .degree.F. COIL
______________________________________ 1 Load Block Off 7.25 psi
13.75 8.5.degree. F. 1 Load Block On 7.50 psi 13.50 8.0.degree. F.
2 Unload Force Off 10.75 psi 10.25 2.0.degree. F. 2 Unload Force On
11.25 psi 9.75 1.0.degree. F. VARIABLE .DELTA.P BLOCK-ABOVE SET
POINT STEP FUNCTION .DELTA.P COIL PSIG .degree.F. COIL
______________________________________ 1 Unload Block On 6 psi 15.0
11.degree. F. 1 Unload Block Off 6.5 psi 14.5 10.degree. F. 2 Load
Force On 4 psi 17.0 14.degree. F. 2 Load Force Off 4.5 psi 16.5
13.degree. F. ______________________________________
It may be appreciated that the bellows 62 and 64 may be formed
appropriately of a metal having a given spring constant, and
provide between full compression and expansion a differential
pressure range which may vary from 0 to 6 psi to as high as 0 to 70
psi. In that regard, the bellows may comprise brass, phosphor
bronze or stainless steel, obviously, the stainless steel providing
the higher spring constant. Referring to the table above, under an
assumed 20.degree. F. ambient and utilizing R-12 as the refrigerant
for the system and for bulb 70, as the pressure differential
increases to 7.50 psi, load blocking is effected by opening of
microswitch contacts for microswitch 76, thus taking coil 53 of the
load solenoid valve 52 off the line. If, for any reason, the
evaporator pressure continues to go down, the differential
increases and, at the point that 11.25 psi differential exists
between chambers 62, 63 and 65, the further depression of the blade
or bar 72 results in the change of state for microswitch 74, with
the switch contacts closed and with the resultant energization of
the coil 51 of the unload solenoid valve 50. Unloading of the
compressor 12 is initiated, with unloading ceasing when the
pressure differential drops to 10.75 psi. Based on parameters
within the space being conditioned, if the pressure differential
drops to 7.2 psi or if the coil pressure rises to 13.75 psi, then
the load block is removed; if the unit is still operating in the
below set point condition, loading commences. However, assuming
that the system is no longer operating in the below set point
condition but in the above set point condition, the circuit to coil
51 of the unload solenoid valve 50 is open when the pressure
differential reaches 6 psi. If the pressure differential continues
to fall to 4 psi even though unloading has terminated, loading will
be commenced by energization of the circuit through microswitch 86
to the coil 53 of load solenoid valve 52, causing the machine to
start to load-up until a 4.5 psi differential is established, then
loading is terminated. However, if this does not occur and the
pressure differential builds up from 6 psi to 6.5 psi, then the
unload block is removed; if the system is still operating in the
above set point condition, unloading will commence until the
differential is again dropped to 6 psi. This is a fine control, and
the slide valve is in all reality locked in a very limited range.
Thus, it may be appreciated that the .DELTA.T type of control as
provided by the present invention is one in which the compressor
operation is for all practical purposes continuous. By way of the
type of floating, unloading limit, the compressor on/off cycling is
greatly reduced, and the floating, loading block, in the same
manner, prevents over-running of the heat exchangers under
conditions of relatively mild heating requirements.
From the above, it may be obvius that at certain times it would be
desirable to override the variable .DELTA.T control as, for
instance, in a morning pull-up condition for a building or
residence which requires more heat during the day than during the
night. This may be accomplished automatically. However, by
reference to FIG. 2, it can be seen that the present invention
provides a simple manually operated override switch 120 in a line
122 which is in parallel with line 88, and permits energization of
the load solenoid valve coil 53 indifference to energization
through the various microswitches or switches 105 and 109 under
thermostatic control. Closure of the single pull, single throw
switch 120 completes the circuit between control voltage lines 86
to the coil 53. Thus, the loading limit block is cut out of the
circuit for a manually determined period of time. Further, instead
of a thermo bulb providing the means for shifting the movable
contacts 108 and 104 for valves 105 and 109, it is obvious that a
bi-metal strip may be employed within the thermostat, which
bi-metal strip is exposed to ambient and incorporates on it two
hermetically sealed glass cylinders partially filled with liquid
mercury. The glass cylinders are provided with spaced contacts
which are closed by shift in the mercury from one side of the
cylinder to the other under predetermined temperature differential
conditions, which would come about as the bi-metal heats up or
cools down. One of the glass cylinders tips at a given first
temperature for the low temperature setting of the two-step
thermostat, while the other glass cylinder tips at a higher
temperature, with the temperature differential being determined by
the two tip points. The first and second set points of the
thermostat are adjustable with respect to each other as well as
with respect to room temperature. This type of two-stage room
thermostat is commercially available from the Minneapolis Honeywell
Corporation or the like.
It is obvious to one skilled in the art that this invention also
applies to a water (or fluid) source heat pump as well. In the
general case, the entering water (fluid) temperature becomes the
reference which the evaporating temperature is measured against. It
is also obvious that the system described pertains to refrigeration
systems as well as heat pump systems. A refrigeration system, of
couse, is a heat pump in the absolute sense of the term, as heat is
pumped from the refrigerated area to the area where the heat is
being rejected.
While the invention has been particularly shown and described with
reference to a preferred embodiment thereof, it will be understood
by those skilled in the art that various changes in form and
details may be made therein without departing from the spirit and
scope of the invention.
* * * * *